German Auslegeschrift No. 1,165,786 discloses an apparatus which comprises sliding blocks which are pressed against the surface of the work pieces to be welded and supply the welding current and the welding electrode and move at the welding speed, and they consist of two segments which are mutually movable and are closely adjacent in the generally vertical centre plane of the welding gap between the work pieces.
An attempt is made to control the contact force of the two-part sliding blocks on the work pieces to be welded so that the force is always optimum even when the work pieces are irregular in shape, for example if they are curved. To achieve this, the segments are pressed by an elaborate lever apparatus having a single pressure spring on each side. Since the segments are only mutually movable to a limited extent, an effective, regular weld seam cannot be produced where there is a considerable edge mismatch of the two work piece edges to be welded or where there is a considerable mutual inclination of the work pieces. Lateral leakage of the melt cannot be reliably avoided.
German Auslegeschrift No. 1,096,515 and German Patent No. 1,108,352 disclose apparatus with which an effective lateral sealing of the pool is indeed achieved, but since the region positioned directly on the melting line is not cooled sufficiently when the sheets are uneven, considerable fluctuations occur in penetration. The positioning, known from elsewhere, of additional guide paths considerably increases the downtime and is not always suitable.
In the apparatus according to German Pat. No. 2,603,020, an effective sealing against the leakage of the pool is ensured by segmentation of the sliding surfaces, but the contact forces cannot be precisely determined due to the large area over which friction occurs between the individual segments.